Professional Engineering Invoice

Standard payment terms for engineering consultants are Net 30, meaning the client has thirty days from the invoice date to pay. For larger public works or corporate projects, Net 45 or Net 60 may be required, so it is crucial to agree on these terms in your initial contract. For new clients, securing an upfront deposit or retainer of 20 to 50 percent is highly recommended.

Yes, including your PE license number or corporate firm registration in the header reinforces your legal credentials and professional authority. It helps your client's accounts payable team verify that they are paying a licensed professional, which is often a compliance requirement for government and municipal projects. It also adds an extra layer of professionalism to your brand.

Your breakdown should map directly to the deliverables outlined in your initial proposal or contract, using specific phases like 'Feasibility Study' or 'Schematic Design.' Avoid overcomplicating the line items with deep technical jargon, but provide enough specificity so a non-technical project manager can easily understand what was accomplished. Grouping your time by day or sub-task ensures maximum transparency.

You should list sub-consultant fees, such as third-party surveyor or lab testing fees, as separate line items on your invoice. It is standard practice to apply a markup of 5 to 15 percent to these services to cover your coordination and administrative overhead, which should be clearly outlined in your initial contract. Always attach the sub-consultant's original invoice as supporting documentation.